This invention relates to a battery saving method for a selectively called radio receiver and to a selectively called radio receiver operable in a battery saving mode.
For a selectively called radio receiver with a battery included, various manners of battery saving are in practical use. In general, each of such select selectively called radio receivers is rendered alive or put in an active state as an active receiver with the battery switched on and is primarily intermittently activated to achieve the battery saving. Towards such active receivers, a base station transmits a radio signal carrying a preamble and, in successive frame periods, information signals collectively as a transmission signal of a bit or baud rate. Each active receiver begins to receive the radio signal as a reception signal while intermittently activated. Towards the base station, the selectively called radio receiver can send a radio signal which may have a different bit rate.
It will be presumed, as in a format specified by the British Post Office Code Standardization Advisory Group (BOCSAG), that the radio signal for transmission as the transmitted signal comprises, in each frame period, a frame synchronization signal and first or primary through N-th or N-ary codewords, where N represents a predetermined integer, such as sixteen. Each of the frame synchronization signals and the codewords in the frame periods consists of a predetermined number of binary bits, such as thirty-two bits. For each frame period as herein called, a combination of the frame synchronization signal and the first through the N-th codewords is called a batch in the art.
In each frame period, the (n-l)-th and n-th codewords collectively form a p-th or p-ary group, where n is variable between 2 and N, both inclusive, and p is consequently variable between 1 and P or N/2. Irrespective of active and inactive status, the radio receivers are grouped into first through P-th groups. In at least one of the successive frame periods that consecutively appears after the preamble in the radio signal, the codewords of the p-ary group serves as an address signal representative of an address preliminarily assigned to a certain one of the radio receives of the p-th group that will herein be called a particular receiver.
Following the address signal either immediately or with one of the frame synchronization signals interposed, consecutive codewords of the successive frame periods are altogether used as a message signal representative of a message directed to the particular receiver. After reception of one of the frame synchronization signals that immediately follows the preamble as a first synchronization signal, it is ordinally unnecessary for the particular receiver to use other intervening frame synchronization signals. At any rate, such frame synchronization signals, address signals, and message signals are herein collectively called the information signals.
After a certain number of frame periods, the message signal may come to an end for the particular receiver. It is possible in this event to make the codewords of at least one immediately following group carry a new address for a radio receiver of one of the first through the P-th groups. If used to indicate the particular receiver again or a different receiver of the p-th group, the new address is carried by the codewords of the p-ary group or groups which codewords appear after the end of the message signal.
Attention will now be directed to the battery saving in the particular receiver. Intermittently activated by the battery, the particular receiver is first put in an intermittently activated state for selecting the preamble in the reception signal. In the meantime, the particular receiver is said to be in a preamble searching mode of operation. After being detected, the preamble is used to establish bit synchronism between operation of the receiver and the reception signal. With the bit synchronism established, the particular receiver is continuously put in a temporarily continually activated state, or in a frame synchronization signal collating mode of operation. Collated with the bit synchronism kept, the first synchronization signal is used in establishing frame synchronism between operation of the receiver and the reception signal.
With the frame synchronism kept, the particular receiver is usually temporarily deactivated and then activated again by the battery into an address signal collating mode of operation. During the address signal collating mode, the particular receiver is either only once activated during the p-th group in the frame period including the first synchronization signal as a first frame period or repeatedly during the p-ary groups in the frame periods consecutively following the preamble. The address signal collating mode will therefore be referred to alternatively as a synchronously activated state.
With the address signal collated, the particular receiver is put by the battery into a continuously activated state or in a message receiving mode of operation of decoding the message signal into the message. When the message signal comes to an end, the particular receiver is automatically put back into the intermittently activated state. After the end of the message signal, the particular receiver may alternatively be intentionally put into an inactive state with the battery switched off.
While detecting the information signal in one of the frame synchronization signal collating mode, the address signal collating mode or the message receiving mode, the particular receiver may occasionally go out of bit synchronism or be put unintentionally into the intermittently activated state when no radio signal or noise alone reaches the particular receiver due to severe fading or substantial masking of the transmission signal. The receiver may also go out of bit synchronism when a break occurs in the radio signal and/or external disturbances are imposed on the reception signal. Furthermore, the particular receiver may be put into the intermittently activated state if the reception signal is subjected to either a break or noise before the bit synchronism is wholly established. In the intermittently activated state, the particular receiver is incapable of locating the preamble in such an event.
In accordance with the above example of the manner of battery saving, each active receiver detects the bit rate of the reception signal as a detected bit rate in a bit rate detection interval to produce a bit rate detection signal while put in the intermittently activated state. If the detected bit rate coincides with the bit rate given to the radio signal as a predetermined bit rate the bit rate detection is successful. The bit rate detection fails if either no signal or only noise is detected at the receiver in question.
If the bit rate is again successfully detected after the bit synchronism is lost in the particular receiver during the synchronously and the continuously activated states, the detected bit rate is used in restoring the bit synchronism so as to establish the frame synchronism for subsequent continuation of the synchronously and the continuously activated states to collate the address signal and to receive the message signal. The particular receiver is therefore temporarily continuously activated during a frame synchronism recovering interval immediately following production of the bit rate detection signal. While activated, the particular receiver collates the frame synchronization signal as a fresh synchronization signal in one of the successive frame periods that either immediately or subsequently follows production of the bit rate detection signal as a fresh frame period.
If the bit rate is successfully detected while the bit synchronism is not yet wholly established in the particular receiver during progress of the preamble in the reception signal, the detected bit rate is used in completely establishing the bit synchronism. As soon as the preamble comes to its end, the particular receiver is temporarily continuously activated for collation of the first synchronization signal. After establishment of the frame synchronism, the particular receiver collates the address signal and receives the message signal.
The first synchronization signal is collated while the particular receiver is first temporarily continually activated during a one-codeword length. In contrast, the fresh synchronization signal is collated while the particuler receiver is later temporarily continuously activated during the frame synchronism recovering interval which may last from the one-codeword length to as long as one frame period.
Examples of bit rate detection are disclosed by Motoki Ide in U.S. patent application Ser. No. 134,685 filed Oct. 12, 1993, for assignment to the present assignee. In the Ide patent application, the bit rate detection is improved above all in its detection sensitivity. The bit rate detection is given the one-codeword length. The frame synchronism recovering interval is given the one frame period, namely, a seventeen-codeword length according to the format specified by the BOCSAG. The Ide patent application is herein incorporated by reference.
An improved battery saving method is revealed by Masahiro Matai and Hiroyasu Kuramatsu in U.S. patent application Ser. No. 180,360 filed Jan. 12, 1994, (herein after "Matai") for assignment to the present assignee. This Matai patent application will also be incorporated herein by reference. Counterpart patent applications were filed as an EP patent application and national applications in some other countries.
In the Matai patent application, the bit synchronism is established independently of the preamble. In the particular receiver, the preamble is used for detection as the reception signal of the radio signal directed to the first through the P-th groups of receivers. In the Matai et al application, the preamble is searched for during activation for the one-codeword length in contrast to the receiver of Ide in which the particular receiver is put in the intermittently activated state, first only partly, during an eighteen-codeword length or a 576-bit length according to the BOCSAG format.
In the receiver of Matai, the bit rate is detected even if the bit synchronism occasionally collapses as above. In order to give a greater efficiency to the battery saving, the Matai receiver is improved by reducing the bit rate detection duration to only slightly longer than a one-bit length for judgement of whether the bit rate detection appears successful or unsuccessful. Incidentally, the frame synchronism recovery interval is denoted in Matai by a reference symbol Y and is presumably equal to about one frame period, namely the seventeen-codeword length according to the BOCSAG format. It appears in Matai that each bit rate detection interval is equal also to the one frame period.
In the Matai patent application and the prior art described therein, the bit rate detection duration is shorter than the 576-bit length used in the Ide receiver in establishing the bit synchronism. It would therefore be better to say that the Matai receiver and the prior art is put, upon failed establishment of the bit synchronism, in a repeatedly activated state or in a bit rate detection mode of operation in which the particular receiver is activated for the bit rate detection duration repeatedly intermittently at the bit rate detection interval until the bit rate is successfully detected in the reception signal. The detected bit rate is used in recovering or establishing afresh the bit synchronism. In the latter event, the first synchronization signal is collated to establish the frame synchronism. In consideration of both such events, the frame synchronism recovering interval may alternatively be called a frame synchronism establishing interval.
In the manner which will later be described in greater detail, the Matai receiver comprises a receiver section put in the intermittently activated state to establish the bit synchronism and put, immediately following establishment of the bit synchronism, in the temporarily continually activated state to estabish the frame synchronism. Connected to the receiver section, bit rate detecting means is put in the repeatedly activated state, upon an occurrence of a failed establishment of the bit synchronism, to detect the bit rate of the reception signal as the detected bit rate in the bit rate detection period repeatedly at the bit rate detection interval and to produce the bit rate detection signal when the detected bit rate coincides with the predetermined bit rate. Connected to the receiver section and to the bit rate detecting means, control means switches the receiver section into a temporarily continuously for continually activated state of recovering or establishing the frame synchronism before lapse of the frame synchronism establishing interval.
In both the Ide receiver and the Matai receiver, the frame synchronism establishing interval is as long as the one frame period immediately following production of the bit rate detection signal. The radio receiver or the receiver section is consequently kept continuously activated throughout the frame synchronism establishing interval. This adversely affects the efficiency of battery saving.
More particularly, the bit rate detection may appear to be successful if the bit rate detecting means produces the bit rate detection signal by occasionally detecting noise having the predetermined bit rate. In this event, the receiver section is temporarily continually or continuously activated for as long as about one frame in search of the frame synchronization signal which is not in fact present. This results in consumption of an increased average electric current.